Question: Rewrite ${\dfrac{9^{-9}}{9^{7}}}$ in the form ${9^n}$.
Explanation: ${ \dfrac{9^{-9}}{9^{7}} = 9^{-9-7}} $ ${ \hphantom{\dfrac{9^{-9}}{9^{7}}} = 9^{-16}} $